Selective immunoassay for IL-1β

ABSTRACT

The subject invention concerns a novel selective, sensitive, and highly reliable immunoassay for detecting human IL-1β in cultured mononuclear cells or human body fluids. It is a sandwich immunoassay which is useful in diagnostic work to detect IL-1β selectively, for the first time, from among similar lymphokines and other substances known to interfere with bioassays for IL-1.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 08/164,283, filedDec. 7, 1993 now U.S. Pat. No. 5,474,899; which is a continuation ofapplication Ser. No. 07/958,442, filed Oct. 6, 1992, now abandoned;which is a continuation of application Ser. No. 07/496,168, filed Mar.19, 1990, now abandoned, which is a continuation of application Ser. No.07/049,630, filed May 13, 1987, now abandoned.

BACKGROUND OF THE INVENTION

Interleukin-1 (IL-1) is important to the activation of T and Blymphocytes and mediates many inflammatory processes. cDNAs coding fortwo distinct forms of IL-1 have been isolated and expressed; these cDNAsrepresent two different gene products, termed I1-1β (Auron, P. E., Webb,A. C., Rosenwasser, L. J., Mucci, S. F., Rich, A., Wolff, S. M. andDinarello, C. A. 1984! Proc. Natl. Acad.

Sci. USA 81:7909) and IL-1α (Lomedico, P. T., Gubler, U., Hellman, C.P., Dukovich, M., Giri, J. G., Pan, Y. E., Collier, K., Semionow, R.,Chua, A. O. and Mizel. S. B. 1984! Nature 312:458). IL-1β is thepredominant form produced by human monocytes both at the mRNA andprotein level. The two forms of human IL-1 share only 26% amino acidhomology. Despite their distinct polypeptide sequences, the two forms ofIL-1 have structural similarities (Auron, P. E., Rosenwasser, L. J.,Matsushima, K., Copeland, T., Dinarello, C. A., Oppenheim, J. J. andWebb, A. C. 1985! J. Mol. Cell Immunol. 2:169), in that the amino acidhomology is confined to discrete regions of the IL-1 molecule. The twoforms of IL-1 also possess identical biological properties, includinginduction of fever, slow wave sleep, and neutrophilia, T- andB-lymphocyte activation, fibroblast proliferation, cytotoxicity forcertain cells, induction of collagenases, synthesis of hepatic acutephase proteins, and increased production of colony stimulating factorsand collagen. IL-1 also activates endothelial cells, resulting inincreased leukocyte adhesiveness, PGI₂ and PGE₂ (prostaglandins)release, and synthesis of platelet activating factor, procoagulantactivity, and a plasminogen activator inhibitor. Clearly, IL-1 plays acentral role in local and systemic host responses. Because many of thebiological effects of IL-1 are produced at picomolar (pg) concentrationsin vivo, IL-1 production is likely a fundamental characteristic of hostdefense mechanisms.

In view of the multiple biological properties of IL-1 associated withinflammation and catabolic processes, the consequences of high levels ofIL-1 in localized tissues such as bone and articular spaces are majorconcerns in the management and treatment of inflammatory diseases.Considerable attention has focused, therefore, on understanding themechanisms of IL-1 production, and the precise function of IL-1 activityin inflammation. There are, then, two main areas of interest:measurement of IL-1 in body fluids and production of IL-1 from cells invitro. At present, measurement of IL-1 produced in in vivo or in vitrois dependent on bioassays. T-cell assays for IL-1, based on theproduction of lnterleukin-2 (IL-2) or increased responsiveness to IL-2,are highly sensitive and can detect 10-100 pg/ml of IL-1 (Dinarello, C.A., Cannon, J. G., Mier, J. W., Bernheim, H. A., LoPreste, G., Lynn, D.L., Love, R. N., Webb, A. C., Auron, P. E., Reuben, R. C., Rich, A.,Wolff, S. M. and Putney, S. D. 1986! J. Clin. Invest. 77:1734). However,these assays are vulnerable to interferences by several substances,including other lymphokines, such as IL-2 and IL-4 that directlystimulate T-cell division (Fox, D., Schlossman, S. and Reinherz, E.1986! J. Immunol. 136:1945). The responses of endothelial (Bevilacqua,M. P., Pober, J. S., Majeau, G. R., Cotran, R. S. and Gimbrone, M. A.Jr. 1984! J. Exp. Med. 160:618; Dejana, E., Balconi, G., DeCastellarnau, C., Barbieri, B., Vergara-Dauden, M. and de Gaetano, G.1983! Biochim. Biophys. Acta 750:261) and synovial cells (Dayer, J-M, deRochemonteix, Burrus, B., Demczuk, S. and Dinarello, C. A. 1986! J.Clin. Invest. 77:645) can be used to measure IL-1; some of these assaysare adequately sensitive. But, these and other non-T-cell assays are notspecific for IL-1 since the measured responses are also observed withother macrophage products, including tumor necrosis factor (Dinarello,C. A., Cannon, J. G., Wolff, S. M., Bernheim, H. A., Beutler, B.,Cerami, A., Figari, I. S., Palladino, M. A. Jr. and O'Connor, J. V.1986! J. Exp. Med. 163:1433; Beutler, B. and Cerami, A. 1986! Nature320:584).

The measurement of IL-1 present in the supernates from cultured cells invitro can be effected by the transfer into the IL-1 assays of substancesused to either stimulate or suppress IL-1 production. For example,mitogens and adjuvants interfere with T-cell assays, while endotoxinsand other bacterial products often mimic IL-1 activities in vivo.Several pharmacological agents which inhibit IL-1 production alsointerfere with biological assays for IL-1 (Dinarello, C. A., Marnoy, S.O. and Rosenwasser, L. J. 1983! J. Immunol. 130:890). Separating suchagents from IL-1 can be difficult since most of these substances bind toprotein. Prostaglandins and other arachidonic acid metabolites are alsoproduced in cell cultures during stimulation of IL-l production andtheir presence during IL-1 bioassays can either inhibit (Cahill, J. andHopper, K. E. 1984! Int. J. Immunopharmacol. 6:9) or enhance (Kunkel, S.L. and Chensue, S. W. 1985! Biochem. Biophys. Res. Commun. 128:892) IL-1activity. Monocytes themselves also produce polypeptide substances thathave been shown to inhibit IL-1 activity in several assays (Arend, W.P., Joslin, F. G. and Massoni, R. J. 1985! J. Immunol. 134: 3868). Allof these factors show that the determination of IL-1 activity is not astraightforward process or a predictable process. Thus, there is a needin the art for a selective and predictable assay for determining thelevel of IL-1β in human fluids, e.g., serum or urine.

The most widely employed IL-1 bioassay is the thymocyte co-stimulator ormouse lymphocyte activating factor (LAF) assay (Gery, I. and Waksman, B.H. 1972! J. Exp. Med. 136:143). The results of this assay are known tovary with the health and age of the mouse and the presence of thymic andaccessory epithelial cells. Although the murine cloned T-helper cellline, D10.G4.1 exhibits remarkable sensitivity to IL-1 (Kaye, J.,Gillis, S., Mizel, S. B., Shevach, E. M., Malek, T. R., Dinarello, C.A., Lachman, L. B. and Janeway, C. A. Jr. 1984! J. Immunol. 133:1339),these assays are also vulnerable to the presence of interferingsubstances "carried-over" from cell supernates or body fluids. Moreover,the response of these cells to IL-1 is often inconsistent betweentesting laboratories. The inconsistencies may be due to the requirementfor macrophage feeder cells, growth factors and/or culture conditions.Some IL-1 T-cell assays involve a 2-step procedure whereby supernatesare transferred to another cell line in order to measure IL-2 levels(Conlon, P. J. 1983! J. Immunol. 131:1280); this procedure is vulnerableto the presence of IL-2 in the original sample. The immunoassaydescribed herein for IL-1β offers the advantage, for the first time, ofestablishing standard methods for measuring IL-1β and reducing thedifferences which occur because of different responding cells orindividual laboratory practices.

BRIEF SUMMARY OF THE INVENTION

The subject invention concerns a selective, sensitive, and highlyreliable immunoassay for detecting human IL-1β in cultured mononuclearcells or human body fluids. Specifically, the invention is a competitiveimmunoassay for human IL-1β which is, advantageously, monospecific. Morespecifically, the invention is exemplified by use of a radioimmunoassay(RIA) which detects 250 pg/ml of IL-1β. This assay can be used tomeasure IL-1β in a variety of cell supernates which contain substanceswhich interfere with in vitro and/or in vivo IL-1. Further, theinvention assay selectively detects IL-1β in the presence of human serumor urine. The novel IL-1β immunoassay of the invention comprises

(a) labeling of recombinant human IL-1β (rIL-1β) to obtain labeled humanrIL-1β;

(b) separating labeled rIL-1β and free label;

(c) analyzing the peak labeled fraction for binding with excessanti-rIL-1β antibody; and

(d) using the fractions with both the highest specific binding and thelowest non-specific binding in a competitive immunoassay to determinethe level of human IL-1β in cultured mononuclear cells or human bodyfluids.

The RIA exemplified herein (Chart A) uses a radioactive isotope, usuallyI-125, to label a known antigen--here, recombinant human IL-1β. Thislabeled antigen (Ag*) competes with the target non-labeled antigen of aspecimen for the binding site of a given amount of "monospecific"antibody (Ab). The radioactivity of the Ag*-Ab complex inverselyindicates the amount of non-radioactive Ag-Ab complexes in the system,and therefore the amount of the target Ag of the specimen.

This subject competitive inhibition assay, which uses labeled IL-1β, andpolyclonal rabbit antisera produced to recombinant human IL-1β, detects,in an RIA assay, 25 pg/ml of recombinant human IL-1β and 50 pg/ml of pI7 human monocyte IL-1. Advantageously, the assay does not detect humanIL-1α, human interleukin-2, human tumor necrosis factor-α, or humaninterferon-γ. Nearly 100% of IL-1 added to human serum or urine can bequantitatively recovered. Substances such as fetal calf serum,phytohemagglutinin, opsonized Staphylococcus albus or E. coli endotoxindo not affect the assay. Using this assay, human monocyte IL-1β wasmeasured in both the intracellular and extracellular compartments andthe results were unaffected by indomethacin or BW 755C, a lipoxygenaseinhibitor. The assay also detected crude human monocyte IL-1β insupernatants from endotoxin challenged mononuclear cells. The utility ofthe subject process is clearly evident in quantitating human IL-1β inbiological fluids and detection of IL-1 in the presence of otherlymphokines. Further, the sensitivity and specificity of the subjectassay permits the detection of IL-1β in a variety of tissue culturesupernates. The assay detects IL-1β in the presence of PHA(phytohemagglutinin) or endotoxin, substances known to interfere withbioassays for IL-1. PHA can affect T-cell assays by the induction ofIL-2 production while endotoxin mimics IL-1 in a variety of in vivo aswell as in vitro assays.

DESCRIPTION OF THE DRAWINGS

FIG. 1: SDS-PAGE of ¹²⁵ I-labeled IL-1β. The positions of the variousmolecular weight markers is indicated.

FIG. 2: Standard curves for the IL-1β radioimmunoassay with IL-1βstandards diluted in heat inactivated normal human sera (▴--▴), 0.2% BSAin 0.01M phosphate buffered saline (pH 7.5) (∘--∘) and RPMI 1640 with 5%FCS (heat inactivated) (--).

FIG. 3: Standard curves for the IL-1β radioimmunoassay with immediate(∘--∘) and delayed (--) addition of ¹²⁵ I-IL-1β. The lower limit ofdetection for IL-1β was 25 pg with a delayed addition of 125I-IL-1β and75 pg with an immediate addition.

FIG. 4: Standard curves for the IL-1β radioimmunoassay with recombinantIL-1β (∘--∘) and monocyte-derived IL-1 (pI 7) (--) as standardsdiluted in 0.2% BSA in 0.01M phosphate buffered saline (pH 7.5). Nocross reactivity was apparent with IL-1α (100 ng/ml) (Genzyme, Boston,Mass.), tumor necrosis factor-a (50 ng/ml) (gift of Genentech), gammainterferon (1×10⁵ u/ml) or IL-2 (200 ng/ml) (Genzyme) (data not shown).

FIG. 5: IL-1β circulating life in C3H/HeJ mice as determined by theIL-1β radioimmunoassay following an intraperitoneal injection ofrecombinant IL-1β. Following a sham injection or the injection of IL-1βthe mice were bled at the indicated time intervals and the heparinizedplasma assayed for IL-1β. 2 mice in each group. Mice injected withbuffer (∘--∘), (Δ--Δ). Mice injected with 100 μg IL-1β (--), ▴--▴).

FIG. 6: G-50 gel filtration chromatography of human MNC (mononuclearcells) supernates stimulated with heat-killed Staphylococcus albus(Dinarello, C. A., Clowes, G. H. A. Jr., Gordon, A. H., Saravis, C. A.and Wolff, S. M. 1984! J. Immunol. 133:1332).

The supernate was concentrated (20-fold) in 3.5 KD dialysis tubingagainst PEG (6-8,000) and applied to a 30×1.0 cm column. The column waseluted in RPMI and each fraction was assayed directly in the RIA andafter a 1:250 and 1:500 dilution, assayed for biological activity inD10.G4.1 cells ((Kaye et al. supra).

DETAILED DISCLOSURE OF THE INVENTION

Following are examples which illustrate procedures for practicing theinvention. These examples should not be construed as limiting. Allpercentages are by weight and all solvent mixture proportions are byvolume unless otherwise noted.

Example 1--Recombinant human IL-1β and production of rabbit antisera

The recombinant IL-1β protein was expressed in E. coli and the 17,000dalton peptide was produced by endoproteolytic cleavage, representingthe 152 amino acid carboxy terminal portion of the 31 kD precursormolecule (Auron, P. E., Webb, A. C., Rosenwasser, L. J., Mucci, S. F.,Rich, A., Wolff, S. M. and Dinarello, C. A. 1984! Proc. Natl. Acad. Sci.USA 81:7909; Dinarello, C. A., Cannon, J. G., Mier, J. W., Bernheim, H.A., LoPreste, G., Lynn, D. L., Love, R. N., Webb, A. C., Auron, P. E.,Reuben, R. C., Rich, A., Wolff, S. M. and Putney S. D. 1986! J. Clin.Invest. 77:1734). Antibodies to rIL-1β were elicited in New Zealandwhite rabbits by the intradermal injection of 100 μg rIL-1β in completeFreund's adjuvant on day 0. On day 40 the animals received asubcutaneous booster injection of 25 pg in incomplete Freund's adjuvant.A second, third and fourth booster injection followed on day 50, day 106and day 189. The animals were bled on day 203 for use of the sera in theradioimmunoassay. This antiserum specifically neutralized human IL-1βwhen tested in either T-cell (Kaye et al. supra) or endogenous pyrogenassays (Dinarello et al. 1986! J. Clin. Invest. 77:1734). When testedagainst recombinant-human IL-1α, no neutralizing effect was observed ineither T-cell or endogenous pyrogen assays.

Example 2--Iodination and purification of labeled rIL-1β

rIL-1β was iodinated to a specific activity of 15 uCi/μg by amodification of the Chloramine T method (Hunter, W. M. and Greenwood, F.C. 1962! Nature 194:495). To about 10 μg of rIL-1β (435 μg/ml) in about0.5M sodium phosphate buffer, pH 7.4, was added about 0.5 mCi Na ¹²⁵ I(100 mCi/ml, Amersham Corporation, Arlington Heights, Ill.); about tenμg chloramine T (2.5 mg/ml, Kodak, Rochester, N.Y.) in 0.5M sodiumphosphate buffer, pH 7.4 was added to the mixture. The mixture wasmanually shaken for about 10 sec; about 100 μg sodium metabisulfite (5.0mg/ml) in about 0.5M sodium phosphate buffer pH 7.4 was added to stopthe reaction. The loss of ¹²⁵ I-IL-1β on the walls of the vials wasprevented by adding about 0.3 ml of 0.2% BSA (Sigma, St. Louis, Mo.) inabout 0.01M phosphate buffered saline, pH 7.4. Immediately after theiodination procedure, the mixture was applied to a 0.6×30 cm column ofG-25 SEPHADEX (Pharmacia, Piscataway, N.J.) previously equilibrated inabout 0.2% BSA (Sigma) in about 0.01M phosphate buffered saline (pH7.4). The ¹²⁵ I-rIL-1β and free ¹²⁵ I were separated on the column withthe same buffer. An aliquot of each 0.5 ml fraction was counted in agamma spectrometer. The peak radioactive fractions were analyzed forbinding with excess anti-rIL-1β antibody; Eighty to ninety per cent ofthe iodinated protein was bound by excess anti-IL-1β antibody while lessthan 8% was bound by normal rabbit serum (non-specific binding). Thefractions with both the highest specific binding and the lowestnon-specific binding were used in the radioimmunoassay. FIG. 1illustrates the purity of the ¹²⁵ I-labeled IL-1β following sodiumdodecyl sulfate polyacrylamide gel electrophoresis (SDS PAGE) (Laemmli,V. K. 1970! Nature (Lond.) 277:680).

Example 3--Radioimmunoassay

All assays were performed in duplicate in 12×75 mm polystyrene tubes.Both simultaneous and sequential assays were used. In the simultaneousassay, about 0.1 ml of a rIL-1β standard in normal human serum, tissueculture media (RPMI 1640) or 0.2% BSA, about 0.15M sodium chloride,about 0.01M sodium phosphate buffer, pH 7.4 (assay buffer) was added toeach tube. Fifty μl of ¹²⁵ I-rIL-1β in assay buffer containing 4% normalrabbit serum were added followed by about 0.1 ml rabbit anti-rIL-1βserum diluted appropriately in the assay buffer. The tubes were shakenand allowed to incubate for about 18 hr at about room temperature (23°C.)

The sequential assay differed from the simultaneous assay in that the¹²⁵ I-rIL-1β was added about 18 hr after the rIL-1β standard andantiserum were mixed; the mixture was then incubated for an additional24 hr at about room temperature (23° C.). In both assays the separationof antibody bound from free ¹²⁵ I-rIL-1β was accomplished by theaddition of about 1.0 ml 6% polyethylene glycol (mol wt--8000) in about0.001M sodium phosphate buffer (pH 7.4) containing about 2.5% sheepanti-rabbit IgG serum (Pel-Freez, Rogers, AR). The tubes were agitated,centrifuged at 1000× g for 15 min at room temperature; the supernatantswere removed by aspiration, and the precipitates counted in an automatedgamma spectrometer for about 1 min. Non-specific binding was determinedby substituting normal rabbit serum at a corresponding dilution in placeof the antiserum.

Example 4--Human cell supernates

Blood from normal human subjects was separated on FICOLL-HYPAQUE(Pharmacia) and mononuclear cells (MNC) were suspended in Eagle'sminimal essential medium containing 100 μg/ml streptomycin. 100 U/mlpenicillin, 0.01M 4-(2-hydroxyethyl)-1-piperazine ethanesulfonic acid(HEPES) buffer (all from Microbiological Associates, Walkersville, Md.)at a concentration of about 5×10⁶ cells/ml. Heat-inactivated AB serumwas added to a final concentration of about 1%. One hundred μl of thecell suspension was added to flat bottom microtiter wells (Nunc,Rotskilde, Denmark) and 100 μl of either control medium or mediumcontaining various substances were added. After about 24 hr ofincubation at about 37° C., the supernates were removed. The cells werethen frozen (about -70° C.) in about 200 μl of fresh culture medium.Three freeze-thaw cycles were used to extract the intracellularmaterial; the lysate was then centrifuged at about 10,000× g for about 5min at 4° C. All extracellular and intracellular materials were frozenat about -70° C. until they were assayed.

Example 5--IL-1 bioassays

Murine thymocytes and a subclone of the murine T-cell line D10.G4.1(Kaye et al. supra) were used to assay IL-1. The D10.G4.1 cells are fromabout 50-100 times more sensitive to stimulation by IL-1 than arethymocytes (Kaye et al. supra). The rabbit endogenous pyrogen assay wasused as previously described (Dinarello, C. A. 1986! J. Clin. Invest.77:1734).

Following are examples illustrating the use of the invention process:

Example 6

To determine the utility of the invention process in measuring actualclinical samples, tests were made of plasma from mice injectedintraperitoneally with rIL-1α. The rIL-1β detected in the circulation ofthese mice is shown in FIG. 5. For this experiment, the rIL-1β standardswere diluted in fresh frozen normal mouse plasma. These and the resultsin Table I demonstrate the usefulness of this assay for thedetermination of rIL-1β levels following parenteral injection.

Example 7

The invention process also can be used to detect IL-1β produced in humanmononuclear cells stimulated with endotoxin, opsonized Staphylococcusalbus, or PHA. In addition, agents such as indomethacin or BW 755C(Dinarello et al., 1983, supra), which interfere with T-cellproliferation assays do not interfere with the invention process. Theeffects of both stimulatory substances as well as inhibitory factors inthe bioassays for IL-1 can be overcome by the use of the inventionprocess see Table II.

Example 8--Use of the invention process to detect various molecularweight fragments of IL-1β

Several molecular sizes of IL-1β have been described using variousbiological assays. There are data that suggest the large molecularweight IL-1's are less potent in various bioassays. Since the process ofthe subject invention detects IL-1β as antigen rather than as abiologically active molecule, the quantitation of IL-1β at variousmolecular weights, in different cell compartments and under conditionsof protease inhibition can be determined (Lepe-Zuniga, J. L., Zigler, J.S. Jr., Zimmerman, M. L. and Gery, I 1985! Mol. Immunol. 22: 1387). IL-1from adherent human blood monocytes stimulated with opsonizedStaphylococcus albus (Dinarello, C. A., Bendtzen, K. and Wolff, S. M.1982! Inflammation 6:63) was chromatographed over SEPHADEX G-50(Pharmacia) and each fraction was assayed for biological activity onD10.G4.1 cells and in the invention process. The results illustrated inFIG. 6 indicate that the invention process can be used to detect IL-1with a variety of molecular weights.

In performing the invention assay using the above materials and methods,the following results were obtained:

(1) Binding of ¹²⁵ I-rIL-1β to anti-IL-1β

A comparison of the binding inhibition curves obtained when the rIL-1βstandards are diluted in assay buffer, culture medium (RMPI 1640) andserum is shown in FIG. 2. The curves derived using the sequential assayprocedure were virtually super-imposable. For the most accuratedetermination of the quantity of IL-1β the rIL-1β standards were dilutedin the same medium as the unknown samples.

FIG. 3 shows the binding inhibition curves obtained using the humanserum based standards in both the simultaneous and sequential assays. Asubstantial displacement of labeled rIL-1β occurred when more than 25 pgrIL-1β was added in the sequential assay, while a similar displacementwas observed at IL-1β levels greater than 75 pg in the simultaneousassay.

(2) Specificity of RIA for human IL-1β

The antiserum used in the assay was shown to be specific for rIL-1β inthat it lacked cross reactivity with rIL-1α (100 ng/ml), rIL-2 (200ng/ml), rTNFα (50 μg/ml), and IFNy (1×10⁶ u/ml) (Table I). Shown inTable I is the nearly complete recovery of IL-1 when added to andincubated with fresh frozen human serum and urine. Human serum and urineare known to contain inhibitory substances that prevent the detection ofIL-1 in most in vitro biological assays unless separated from the IL-1.

Using the thymocyte co-mitogenesis assay, ten half maximal units/ml ofpurified monocyte IL-1 (pI 7) and recombinant IL-1β gave a displacementequal to 0.4 ng/m-L and 1.0 ng/ml rIL-1β, respectively. These resultsreflect the differences in specific activity of the two IL-1preparations (purified monocyte-derived IL-1 2.5×10⁷ U/mg! and rIL-1β1×10⁶ U/mg!)(Dinarello et al. 1986! J. Clin. Invest. 77:1734). FIG. 4compares the competitive inhibition curves of rIL-1β and purifiedmonocyte IL-1, pI 7, in the RIA.

The invention assay, described above, can be carried out usingalternative procedures. These other embodiments of the invention are asfollows:

1. Radiolabel IL-1β with ¹²⁵ I via the ¹²⁵ I-Bolton-Hunter reagent(Bolton, A. E. and Hunter, W. M. 1973! Biochem. J. 133:529-539). UseI-IL-1β as described in Example 2.

2. Immobilize anti-IL-1β on a solid support. Label IL-1β with an enzymeor fluorogenic material. Use these reagents in a competitive bindingassay.

3. Immobilize rabbit anti-IL-1β on a solid support. Label rabbitanti-IL-l with an enzyme or fluorogenic material. Use these reagents to"sandwich" IL-1β present in sample.

4. Immobilize mouse monoclonal anti-IL-1β on a solid support. Labelrabbit anti-IL-1β with an enzyme or fluorogenic material. Use thereagents to "sandwich" IL-1β present in sample.

5. Immobilize mouse monoclonal anti-IL-1β on a solid support. "Sandwich"IL-1β present in sample with rabbit anti-IL-1β. Add radioisotope, enzymeor fluorogenic material labeled anti rabbit IgG to detect rabbitanti-IL-1β. This signal is proportional to the amount of IL-1β. Thisassay, known as the enzyme linked immunosorbent assay (ELISA) can becarried out as follows:

100 μl of a monoclonal antibody specific for IL-1β appropriately dilutedin 0.01M sodium phosphate buffer, pH 7.4 was passively adsorbed to apolystyrene microtiter plate. The plate was washed with 0.01M phosphatebuffer, pH 7.4 containing 0.05% Tween-20 after an overnight incubationat 23° C. The plate was subsequently overcoated with 0.01M sodiumphosphate buffer, pH 7.4 containing 1% bovine serum albumin (BSA). Theplate was incubated for 2 hr at 23° C. and washed as described above.

100 μl of a serum, urine culture medium or buffer containing IL-1βsolution was added to the wells of the plate. The plate was incubatedfor 2 hr at 37° C. The plate was washed as described above. One hundredμl of rabbit anti IL-1β serum appropriately diluted in 0.01M sodiumphosphate, 0.15M sodium chloride, pH 7.4, containg 0.2% BSA was added toeach well and incubated for 2 hr at 37° C. The plate was washed asdescribed above. 100 μl of a goat anti rabbit IgG-horseradish peroxidaseconjugate (Pel Freez, Rogers, Ak.) appropriately diluted in assay bufferwas added to each well and incubated for 30 min at 37° C. The plate waswashed as described above.

To develop the color, 100 μl of o-phenylene diamine (0.4 mg/ml) incitrate-phosphate buffer, pH 5.0, containing 0.01% H₂ O₂ was added toeach well. The reaction is stopped by the addition of 50 μl of 4N H₂ SO₄and the plate read in a microtiter plate reader at O.D.₄₁₀.

The quantity of IL-1β in the unknown sample is determined from astandard curve constructed using known quantities of IL-1β, for example,as follows:

    ______________________________________                                               IL-1β                                                                    (ng/ml)                                                                             O. D..sub.410                                                    ______________________________________                                               0.000 0.119                                                                   0.016 0.160                                                                   0.031 0.195                                                                   0.063 0.243                                                                   0.125 0.331                                                                   0.250 0.492                                                                   0.500 0.750                                                                   1.000 1.055                                                            ______________________________________                                    

A kit for the above assay would contain the following:

(1) a microtiter plate with monoclonal antibody specific for IL-1βabsorbed to the wells;

(2) a container of rabbit anti IL-1β antibody;

(3) a container of goat anti rabbit IgG-horseradish peroxidaseconjugate;

(4) a container with interleukin-1β standard;

(5) a tablet of o-phenylenediamine;

(6) a container of H₂ O₂ ;

(7) a container of 4N H₂ SO₄ ; and

(8) a container of wash buffer.

The use of these alternative procedures in the subject invention processis well within the skill of a person in the art. No undueexperimentation would be involved to achieve essentially the sameadvantageous results as disclosed above. Further, it should berecognized that, once the subject concept of the invention is known, itis well within the skill of persons in the art to employ this conceptwith other modifications and achieve essentially the same advantageousresults as disclosed herein. Thus, this invention includes not only thespecific procedures disclosed herein but also all modifications of theseprocedures which give essentially the same results.

A wide variety of solid phase supports can be used to immobilize theanti-IL-1β. For example, suitable supports are dextran and cellulose,and continuous surfaces such as polystyrene and polypropylene discs, orthe walls of plastic or glass tubes or slides. Plastic surfaces exhibitadsorptive properties, and simply exposing such surface to anappropriate dilution of the antibody will lead to the attachment of aproportion of the antibody molecules thereon. The bond is probably ionicor hydrophobic, and not covalent. Covalent bonding, however, can bereadily obtained by the incorporation of cross-linking agents such asglutaraldehyde and other agents in the antibody solution used for thecoating.

Coated tube systems offer great convenience in the actual performance ofassays and the technique can be widely used in commercial kits.

The anti-IL-1β can be labeled with a radioactive material such as ¹²⁵iodine, as disclosed herein; labeled with an optical label, such as afluorescent material; or labeled with an enzyme such as horseradishperoxidase. The anti-IL1β also can be biotinylated and labeled avidinused to detect its binding to the immunoadsorbent.

After incubation with the labeled antibody, the immunoadsorbent isseparated from the solution and the label associated with theimmunoadsorbent is evaluated. Depending upon the choice of label, theevaluation can be done in a variety of ways. The label can be detectedby a gamma counter if the label is a radioactive gamma emitter, or by afluorimeter, if the label is a fluorescent material. In the case of anenzyme, label detection may be done calorimetrically, employing asubstrate for the enzyme.

For convenience and standardization, reagents for the performance of theassay can be assembled in assay kits. A kit for screening body fluids,for example, serum, can include:

(1) a container with interleukin-1β antiserum;

(2) a container with labeled interleukin-1β, for example, ¹²⁵ Iinterleukin-1β; and,

(3) a container with interleukin-1β standard.

A kit also will contain a buffer containing bovine serum albumin (BSA),and polyethylene glycol in separate containers.

An example of a kit for 100 assay tubes including standard curves is asfollows:

1 vial interleukin-1β antiserum; lyophilized; 10 ml afterreconstitution. Rabbit interleukin-1β antiserum in buffered salinecontaining bovine serum albumin. Contains 0.1% sodium azide as apreservative.

1 vial ¹²⁵ I interleukin-1β; lyophilized; 10 ml after reconstitution.Radioactively labeled interleukin-1β in buffered saline containingrabbit serum and bovine serum albumin. Contains 0.1% sodium azide as apreservative. 5 uCi.

1 vial interleukin-1β standard; lyophilized; 0.5 ml afterreconstitution. 50 ng/ml interleukin-1β in buffered saline containingbovine serum albumin. Contains 0.1% sodium azide as a preservative.

1 bottle BSA phosphate buffer; 100 ml; phosphate buffered salinecontaining bovine serum albumin. Contains 0.1% sodium azide as apreservative.

1 bottle Polyethylene Glycol (PEG) Second Antibody; 100 ml; polyethyleneglycol 6000 in phosphate buffer containing anit-rabbit IgG serum.Contains 0.1% sodium azide as preservative.

The reagent preparation for the above kit is as follows:

A. Interleukin-1β antiserum. Reconstitute with 10 ml distilled ordeionized water. Swirl gently to insure that lyophilized reagent on thesides of vial is dissolved. Allow 10 to 15 min for reconstitution.

B. ¹²⁵ I-Interleukin-1β. Reconstitute with 10 ml distilled or deionizedwater. Swirl gently to insure that lyophilized reagent on the sides ofvial is dissolved. Allow 10 to 15 min for reconstitution.

C. Interleukin-1β standard. Reconstitute with 0.5 ml distilled ordeionized water. Swirl gently to insure that lyophilized reagent on thesides of vial is dissolved. Allow 10 to 15 min for reconstitution. Thesolution contains 50 ng/ml of interleukin-1β. Do not attempt to storethe diluted standards.

D. BSA phosphate buffer. The buffer, based in 0.01M phosphate pH 7.0with 0.2% bovine serum albumin containing 0.1% sodium azide, is suppliedready for use.

E. Polyethylene Glycol (PEG) Second Antibody. This suspension issupplied ready for use. Mix well before using.

The preparation of standards for the above kit is as follows:

The stock solution contains 50 ng/ml. Distribute serial dilutions of thestock standard concentrate into a series of test tubes to achieve thedesired concentrations (suggested range: 5 ng/ml to 0.25 ng/ml) bydilution with the medium, serum or BSA phosphate buffer diluent suppliedwith the kit.* A reasonable dilution scheme is shown below. Preparestandards shortly before use; do not store diluted standards.

5.0 ng/ml--0.1 ml stock plus 0.9 ml buffer

2.0 ng/ml--0.4 ml of 5.0 ng/ml standard plus 0.6 ml buffer

1.0 ng/ml--0.2 ml of 5.0 ng/ml standard plus 0.8 ml buffer

0.5 ng/ml--0.1 ml of 5.0 ng/ml standard plus 0.9 ml buffer

0.25 ng/ml--0.05 ml of 5.0 ng/ml standard plus 0.95 ml buffer

*Standards should be prepared in the same diluent as the test samples.

The assay procedure for the above kit, which should be read in itsentirety before beginning the assay, is as follows:

1. Label test tubes for the six interleukin-1β standards, total count(TC) tubes, non-specific binding (NSB) tubes, test samples andappropriate controls. Standards, controls, TC and NSB tubes should betested in duplicate.

2. Pipette 100 μl of each standard, control and test sample into theproper tube. The NSB tubes should receive the zero standard.

3. Add 100 μl of the interleukin-1β antiserum to each tube except the TCand NSB tubes. (Add 100 μl of buffer to the NSB tubes). Mix byvigorously shaking the test tube rack ten times or by vortex mixing eachtube.

4. Allow tubes to stand for 16-24 hr at room temperature (20° C. to 30°C.).

5. Add 100 μl of the ¹²⁵ I-interleukin-1β to each tube, including the TCtubes. Set the TC tubes aside at room temperature (20° C. to 30° C.)until Steps 6 through 9 are completed. Mix by vigorously shaking thetest tube rack ten times or by vortex mixing each tube.

6. Allow tubes to stand for 16-24 hr at room temperature (20° C. to 30°C.).

7. Add 1.0 ml PEG-Second Antibody Solution to each tube except the TCtubes. Mix thoroughly on a vortex-type mechanical mixer for 3 to 5 sec.

8. Centrifuge all tubes except the TC tubes at a minimum of 1000× g for15 min. The tubes need not be centrifuged in a refrigerated centrifuge,although that is an acceptable option.

9. Aspirate or decant completely each tube, except the TC tubes, withoutdisturbing the precipitate. If a decanting procedure is used, inverttubes with a smooth motion and gently blot against absorbent paper toremove residual droplets.

10. Place all tubes in a gamma counter. Determine the level ofradioactivity in each tube. Extending the counting time generallyimproves the accuracy of gamma counter results.

Alternate assay procedure

For an overnight yet less sensitive assay, follow Steps 1, 2, and 3 inthe assay procedure, omit Step 4, and follow steps 5 through 10. Thisprocedure will yield an assay with a minimal detection limit of 1.0ng/ml interleukin-1β.

The calculations and plotting for the above assay are as follows:

1. Calculate the average counts for each set of duplicate tubes.

2. Calculate the average net counts by subtracting the average of theNSB tubes.

3. Calculate the percent B/Bo for all standards and samples as follows:##EQU1## 4. Construct a standard curve by plotting the average percentbound for each standard on the vertical (Y) axis and the correspondingdose value on the horizontal (X) axis. Construct the curve of best fitthrough the points.

5. The amount of interleukin-l in each sample is determined byinterpolation from the standard curve.

Note: Samples with concentration greater than the range of the standardcurve must be diluted in the appropriate solution and reassayed todetermine the precise concentration of interleukin-1β.

Typical data for the above assay are as follows:

    ______________________________________                                                           CPM                                                        Tube               Minus     Avg.  % B-                                       Number                                                                              Sample I. D. Background                                                                              CPM   NSB/T % B/Bo                               ______________________________________                                        1     Total Counts (TC)                                                                          19594     19514                                            1     Total Counts (TC)                                                                          19433                                                      2     NSB           760       738  (4.0)                                      2     NSB           726                                                       3     Zero Standard                                                                              6845      6838  31.3                                       3     Zero Standard                                                                              6831                                                       4     0.25 Standard                                                                              6366      6323  28.6  91.3                                 4     0.25 Standard                                                                              6281                                                       5     0.50 Standard                                                                              5884      5879  26.3  84.0                                 5     0.50 Standard                                                                              5875                                                       6     1.00 Standard                                                                              5011      4965  21.7  69.3                                 6     1.00 Standard                                                                              4920                                                       7     2.00 Standard                                                                              3336      3220  13.2  42.2                                 7     2.00 Standard                                                                              3305                                                       8     5.00 Standard                                                                              1503      1517  4.0   12.8                                 8     5.00 Standard                                                                              1531                                                       ______________________________________                                    

Performance characteristics of the above assay are as follows:

Sensitivity

The lowest concentration of interleukin-1β reproducibly detectable fromthe zero level (95% confidence) is 0.25 ng/ml.

Specificity

The antiserum used in this assay was shown to be specific forinterleukin-1β. No cross reactivity was apparent with interleukin-1α,interleukin-2, tumor necrosis factor, or interferon-γ.

                  TABLE I                                                         ______________________________________                                        Recovery of rIL-1β Added to Human Serum and Urine                              Initial rIL-1β                                                                     rIL-1β added                                                                        rIL-1β measured                                                                    Recovery                                 Sample                                                                              (ng/ml)   (ng/ml)    (ng/ml)   (%)                                      ______________________________________                                        Serum                                                                         #1    0         1.0        1.08      108                                      #2    0         1.0        1.02      102                                      #3    0         1.0        1.08      108                                      #4    0         1.0        0.93       93                                      #1    0         0.5        0.53      106                                      #2    0         0.5        0.52      104                                      Urine                                                                         #1    0         1.0        1.13      113                                      #2    0         1.0        1.17      117                                      #1    0         1.45       1.35       93                                      #2    0         1.45       1.43       99                                      ______________________________________                                    

                  TABLE II                                                        ______________________________________                                        Comparison of the Measurement of IL-1                                         from Cultured Mononuclear Cells                                                               Bioassay   Radioimmunoassay                                   Preparation     (Units/ml IL-1)                                                                          (ng/ml IL-1β)                                 ______________________________________                                        Human MNC                                                                     unstimulated     10        <.2                                                + ET 20 ng/ml   175        9.8                                                + ET 10 ng/ml   150        9.7                                                + ET 5 ng/ml    160        8.5                                                + ET 1 ng/ml    170        4.2                                                + PHA 30 ug/ml  400        10.5                                               + PHA 3 ug/ml   300        7.8                                                + Staph. albus  150        35.0                                               unstimulated     0         <0.2                                               + ET 20 ng/ml   150        14.0                                               + ET 10 ng/ml   150        15.0                                               + ET 5 ng/ml    160        12.0                                               + PHA 30 ug/ml  500        16.0                                               + PHA 3 ug/ml   400        3.5                                                + Staph. albus  200        50.0                                               unstimulated     20        <0.2                                               + ET 1 ng/ml    120        2.4                                                + ET 1 ng/ml + Indo*                                                                          250        3.0                                                + ET 1 ng/ml + BW755C**                                                                        20        1.8                                                unstimulated (intracell)                                                                       0         <0.2                                               unstimulated (extracell)                                                                       10        <0.2                                               + ET 1 ng/ml (intracell)                                                                       80        2.4                                                + ET 1 ng/ml (extracell)                                                                      100        1.8                                                unstimulated (intracell)                                                                       10        <0.2                                               unstimulated (extracell)                                                                       20        <0.2                                               + ET 10 ng/ml (intracell)                                                                     220        0.3                                                + ET 10 ng/ml (extracell)                                                                     160        2.5                                                ______________________________________                                         *1 uM                                                                         **10 uM                                                                       ##STR1##                                                                  

I claim:
 1. A method for detecting human interleukin-1β (IL-1β) in asample, comprising contacting said sample with a first antibody thatimmunoreacts with IL-1β, wherein said first antibody is immobilized on asolid support and forms an immune complex with IL-1β in said sample, andcontacting said immune complex with a second antibody that immunoreactswith IL-1β, and detecting said second antibody bound to said immunecomplex, wherein said second antibody is an antibody, or antigen-bindingfragment thereof, that binds specifically to human IL-1β and does notbind to human IL-1α, human IL-2, human tumor necrosis factor-α, or humanγ-interferon, and binds to human IL-1β in the presence or absence ofphytohemagglutinin and endotoxin.
 2. The method according to claim 1,wherein said first antibody is a monoclonal antibody.
 3. The methodaccording to claim 1, wherein said second antibody is a polyclonalantibody.
 4. The method according to claim 1, wherein said secondantibody is labelled with a detectable signal generating system, whereina signal from said system is detectable.
 5. The method according toclaim 4, wherein said signal generating system is selected from thegroup consisting of radioisotopes, enzymes and fluorogenic compositions.6. The method according to claim 1, wherein said second antibody boundto said immune complex is contacted with a moiety that binds to saidsecond antibody, wherein said moiety is labelled with a detectablesignal generating system, wherein a signal from said system isdetectable.
 7. The method according to claim 6, wherein said signalgenerating system is selected from the group consisting ofradioisotopes, enzymes and fluorogenic compositions.
 8. The methodaccording to claim 1, wherein said solid support is selected from thegroup consisting of dextran, cellulose, plastic and glass.
 9. The methodaccording to claim 1, wherein said second antibody is biotinylated andsaid second antibody bound to said immune complex is contacted withavidin linked to a detectable signal generating system, wherein a signalfrom said system is detectable.
 10. The method according to claim 9,wherein said signal generating system is selected from the groupconsisting of radioisotopes, enzymes and fluorogenic compositions.
 11. Akit for performing an assay for detecting IL-1β in a sample, comprisingin one or more containers: a) a first antibody that immunoreacts withIL-1β;b) a second antibody that immunoreacts with IL-1β wherein saidsecond antibody is an antibody, or antigen-binding fragment thereof,that binds specifically to human IL-1β and does not bind to human IL-1α,human IL-2, human tumor necrosis factor-α, or human γ-interferon, andbinds to human IL-1β in the presence or absence of phytohemagglutininand endotoxin.
 12. The kit according to claim 11, further comprising:c)an IL-1β standard.
 13. The kit according to claim 11, wherein said firstantibody is a monoclonal antibody.
 14. The kit according to claim 11,wherein said second antibody is a polyclonal antibody.